1. Field of the Invention
The present invention relates to a fluoroaluminosilicate glass powder enabling to improve an acid resistance of a dental glass ionomer cement, and a production method thereof.
2. Description of the Conventional Art
The dental glass ionomer cement has excellent affinity for a living body, adhesion to tooth structure, and excellent esthetics since a set body is translucency. In addition, the dental glass ionomer cement has a merit that the cement slowly releases fluoride to strengthen a tooth structure, so that it has been widely used in various applications of dental field. The dental glass ionomer cement is a dental cement including a fluoroaluminosilicate glass powder and polycarboxylic acid aqueous solution as main components. More particularly, the polycarboxylic acid aqueous solution dissolves a surface one layer of the fluoroaluminosilicate glass powder and liberates metals in the glass (alkali metal, alkali-earth metal, and aluminum) as ions. These ions combine with a carboxyl group in the polycarboxylic acid by ionic bonding and form a crosslinking structure to be set by gelation (hereinafter, it may be called as an ionomer reaction).
However, it is known that, after setting, the dental glass ionomer cement is dissolved a little by an acid. It is thought that this reaction is not a problem in general, but by cases, it is concerned that the reaction becomes a problem in some portions, such as a space between teeth and a space of a dental restorative material, where the concentration of an acid has become extremely high by caries. Therefore, it is desired to develop a dental glass ionomer cement having higher acid resistance.
The present inventors confirmed that when a fluoroaluminosilicate glass powder containing lanthanum is used, the glass and a matrix after setting are chemically stabilized and acid resistance improves (refer to Japanese Patent Application Laid-Open No. H5-331017 and Japanese Patent Application Laid-Open No. H6-321724). However, there is a problem that when lanthanum having a large ionic radius is contained in a glass, the refractive index of the glass powder becomes high and the difference of the refractive index to the polycarboxylic acid aqueous solution, which is cement liquid, becomes large, so that the transparency of the set body lowers.